An x-ray tube comprises an envelope, an anode target rotatably mounted within the envelope, and a cathode and window assembly mounted within the envelope and spaced relative to the anode. Each of the grind spindles include two independent grinding wheels driven by a single spindle drive. The cap is rotatably mounted on the hollow base of the container to present the solid product to a surface of application including skin, face, lip, eyelashes, hair, nail etc. When a network device belonging to the device group A is newly installed and the power supply is turned on, the network device issues a Hello message indicating entry to the network. Also, a VUV gas discharge lamp, a photo-ionization device and a photo-ionization detector comprising said transmission window are defined.